The present invention relates to an infrared ray sensor for measuring the temperature of an object whose temperature is to be measured in a non-contact state and a method of manufacturing such as infrared ray sensor.
Infrared ray sensors designed to form an infrared ray detecting element (temperature sensing element) on a bridge above a substrate are known. Such infrared ray sensors exhibiting an improved sensitivity have been proposed in, for example, Japanese Patent Laid-Open Nos. 178149/1982 and 277528/1987.
Infrared ray sensors designed to provide a plurality of infrared ray detecting elements on bridge substrates have also been proposed. In such infrared ray sensors, infrared radiation is made incident on half of the plurality of infrared ray detecting elements while it is not made incident on the remaining half thereof, and the difference in the two outputs is calculated. Consequently, adverse effect of the disturbance can be eliminated, and sensitivity can thus be improved.
Such conventional infrared ray sensors, having a plurality of infrared ray detecting elements so that a difference between the output of the infrared ray detecting element to which infrared radiation is made incident and that of the infrared ray detecting element to which no infrared radiation is made incident can be produced, have the following concrete configuration.
That is, two ceramic substrates each of which has an infrared ray detecting element formed thereon are accommodated in a hermetic package having a window through which infrared radiation enters. One of the substrates is connected to the distal ends of the terminal pins of the hermetic package in a state in which the infrared ray detecting element thereof faces the window so that infrared radiation can enter the element. The other substrate is connected to the distal ends of the terminal pins of the hermetic package at a position separated from the window so that no infrared radiation enters its infrared ray detecting element. The difference in the output between the two infrared ray detecting elements is calculated, by which adverse effect of the disturbance can be eliminated.
In recent years, attempts have been made to manufacture supersmall infrared ray sensors by utilizing the semiconductor microfabrication technologies. Photolithographic and etching technologies are used to form very small bridge structures on each of which an infrared ray detecting element is formed. In this sensor, the bridges each of which has the infrared ray detecting element formed thereon are formed on one surface of the sensor substrate, and infrared radiation is detected from the difference in the output between the infrared ray detecting element on which infrared radiation is made incident and the infrared ray detecting element on which no infrared radiation is made incident, as in the former infrared ray sensor.
However, the above-described conventional infrared ray sensors have the following drawbacks.
In the configuration of the type in which the substrates are accommodated in the hermetic package, connection of the individual substrates to the terminals of the hermetic package makes manufacture of the sensor very difficult in terms of workability and reproducibility of the position of the elements.
Furthermore, one of the infrared ray detecting elements must be disposed at the position where it does not face the window of the hermetic package in a state where it is separated from the package case through a predetermined distance. Also, it is difficult to maintain the positional relation between the two infrared ray detecting elements in an adequate state. This causes a slight amount of infrared radiation to be made incident on the infrared ray detecting element to which no infrared radiation is to be made incident. The amount of infrared radiation which is incident on that infrared ray detecting element varies depending on the sensors. These necessitate inspection and correction to be made on the assembled sensors, thus increasing amount of labor required to manufacture an infrared ray sensor exhibiting excellent characteristics.
In the conventional infrared ray sensor manufactured by utilizing the semiconductor microfabrication technologies, it is very difficult to make infrared radiation incident on one of the infrared ray detecting elements and to make no infrared radiation incident on the other because of its very small size. Accordingly, it is practiced to form a film made of a material which reflects infrared radiation, such as gold (Au) on one of the bridges.
However, provision of the reflecting film on the bridge changes the heat conducting state of the individual bridges, and this makes production of real difference in the output impossible. It is therefore difficult to obtain a stable output, because of the advance effect of the disturbance.
Also, in the latter conventional infrared ray sensor, the bridges and the substrates are made of the same material from the viewpoint of facilitation of manufacture and provision of strength. In this case, since there is no difference in the coefficient of thermal conductivity between the silicon substrates and the infrared ray detecting elements, the light receiving area of the sensor must be increased in order to obtain an output at a sufficient level. Alternatively, the portion of the sensor from which heat escapes must be reduced. Conventionally, it is therefore difficult to reduce the size of the sensor device.
To achieve reduction in the size of the sensor device, the bridges are formed of a material having a smaller coefficient of thermal conductivity than the substrate material. If the substrates are made of silicon, silicon oxide or silicon nitride film may be used.
However, in the infrared ray sensor having the above-described structure, stress may be generated in the film during the manufacturing process due to a difference in the coefficient of thermal expansion between the silicon substrate and the silicon oxide or silicon nitride film. This leads to breakage of the bridge. To prevent breakage, a laminated configuration of the silicon oxide or silicon nitride film which is capable of cancelling the stress may be adopted. However, such a laminated configuration is complicated, and is readily affected by variations in the film thickness, resulting in decrease in the yield of the manufacture of bridge structure. Also, manufacture of such a film requires the very troublesome process.
For selective etching of the laminated film made of silicon oxide and that of silicon nitride, which is conducted to obtain in the bridge structure, different etchants and different etching conditions are used. This makes etching process complicated and difficult.